The present invention relates to the art of endodontic instruments such as files and reamers for use in performing root canal therapy on a tooth and, more particularly, to improved instruments for the latter purpose.
It is of course Well known that the field of endodontics relates to the cleaning and enlargement of the root canals of human teeth for the purpose of removing organic materials and extraneous material present in the root canal and for enlarging the canal so that it can be filled. The diameter of the canals inside the root or roots of a tooth is very small, ranging from about 0.06 mm to about 0.2 mm at the apical tip. In order to perform the necessary therapy on the tooth, the upper end of the tooth is opened to access the hollow portion of the tooth, and a series or set of root canal files and/or reamers are utilized to remove the infected tissue within the canals and to enlarge the canals whereby the latter become mechanically sterilized and rendered large enough to receive the root canal filling material.
Two basic varieties of such endodontic instruments have been available heretofore for such root canal therapy, one of which is a tapered wire, usually of stainless steel or a nickel-titanium alloy, which is ground flat on three or four sides to provide a triangular or square cross-section, and which is then twisted to create a three-dimensional file with sharp edges and flutes between the edges. Examples of such endodontic files are shown for example in patents U.S. Pat. No. 4,443,193 to Roane, U.S. Pat. No. 4,536,159 to Roane, and U.S. Pat. No. 4,611,508 to Roane, which patents are hereby incorporated herein by reference for background purposes. The second variety of such endodontic instruments is formed using the same tapered wire of stainless steel or a nickel-titanium alloy, but the wire is hollow ground to provide cutting edges thereabout as opposed to being ground flat and twisted to provide the cutting edges. Examples of endodontic instruments in the latter category are shown, for example, in patents U.S. Pat. No. 4,299,571 to McSpadden, U.S. Pat. No. 4,332,561 to McSpadden, U.S. Pat. No. 4,934,934 to Arpaio, et al., U.S. Pat. No. 5,464,362 to Heath, et al., and U.S. Pat. No. 5,762,541 to Heath, et al., which patents are hereby incorporated herein by reference for background information. These instruments can be hand-operated for cutting in a tooth canal during the down or up stroke of the instrument in the canal, or they can be rotated such as through the use of powered drilling instruments.
Such endodontic files and reamers heretofore available are used in sets in which the tools increase in diameter from one to the next in the set. Among the disadvantages of such instruments is the fact that the sets are produced by different manufacturers and, accordingly, come in different sizes, shapes and the like. Moreover, too many individual or different instruments are required in order to achieve a desired canal therapy. For example, there are three standard lengths for the files, namely 21, 25 and 31 mm, and at least 26 widths or diameters are available from 0.06 mm to 1.4 mm. Furthermore, in order to assure having the ability to achieve a desired canal therapy in view of the differences in patient""s teeth, a dentist may use several different brands of such instruments, whereby the cost of obtaining and maintaining a sufficient supply is undesirably high. This will be appreciated when it is realized that the cost of such instruments is in the range of $1.25 each to over $6.50 each, and the fact that it is not unusual to utilize 10 to 20 instruments for a root canal procedure. Still further, some of the instruments can only be used once, and when the flutes between cutting edges of an instrument are filled with debris, the cutting efficiency is drastically reduced. Still further, since many files or reamers in a series are necessary to gradually enlarge the root canal to the desired width, the root canal process is very inefficient and slow. A further disadvantage lies in the fact that root canals are often curved and the files and reamers lack sufficient flexibility to follow the path of the canal and often gauge the tooth laterally outwardly of the canal. The files and reamers are also prone to breakage and separation which leaves a portion of the instrument in the canal, and the removal of such a broken piece of the instrument is very difficult if not impossible and, in any event, very time consuming.
In accordance with the present invention, an improved endodontic instrument for performing root canal therapy is provided and by which the foregoing and other disadvantages of such instruments heretofore available are minimized or overcome. More particularly in this respect, an endodontic instrument in accordance with the invention includes a cutting head having a frusto-conical cutting surface tapering inwardly from a base end to a second end. Preferably, the base ends of successive instruments in a set are of the same diameter while the cutting surfaces have different lengths and different tapers between the base and second end. A follower extends from the second end to the distal end of the instrument to promote the instrument following a curved root canal, and in the last instrument in a set the follower is defined by the apex of the conical cutting surface. Preferably, the cutting surface includes an abrasive such as diamond dust, and the cutting head is integral with or attached to a shaft and is tethered to the shaft by a retaining arrangement which assures that the shaft and cutting head remain interconnected in the event of breakage of the shaft during a root canal procedure, whereby removal of the portion of the instrument in the canal is facilitated. The retaining arrangement advantageously enables the use of a small diameter shaft which increases the flexibility of the instrument and improves the ability of the instrument to follow a curved root canal. Moreover, the retaining arrangement is totally flexible and, preferably, is provided by one or more spring wires helically wound about the shaft and having opposite ends attached one to the cutting head and the other to the shaft. The frusto-conical cutting surface advantageously avoids flutes which can clog with debris and, preferably, opposite sides of the base end of the cutting head are truncated to provide passageways allowing the debris to move outwardly of the canal relative to the instrument. A further advantage is that considerably fewer instruments will be required to perform a given root canal therapy resulting in a considerable savings in the cost of having an undesirably large inventory of such endodontic instruments.
It is accordingly an outstanding object of the present invention to provide an improved endodontic instrument for use in performing root canal therapy on a tooth.
Another object is the provision of an instrument of the foregoing character having a structure which promotes obtaining the desired root canal therapy with fewer instruments than heretofore required.
A further object is the provision of an instrument of the foregoing character having a cutting head and a supporting shaft therefor and wherein an arrangement is provided for precluding complete separation of the cutting head and shaft in the event of breakage during a root canal procedure.
Still another object is the provision of an instrument of the foregoing character in which the cutting head is free of flutes, crevices or the like which can fill with debris during a root canal procedure, thus promoting longer cutting efficiency for the instrument.
Still another object is the provision of an instrument of the foregoing character which enables root canal therapy using fewer instruments than heretofore required and wherein each instrument is highly efficient in connection with the cutting action performed thereby, and wherein retention of a broken portion of an instrument is assured to facilitate removal of the portion of the instrument from a root canal in the event of breakage of the instrument.
Still another object is the provision of an instrument of the foregoing character having a flexibility and structural profile which promotes the instrument following a curved tooth root canal.
Still a further object is the provision of an instrument of the foregoing character wherein the base of the cutting head is of the same diameter for all of the instruments in a set and wherein the length and taper of the cutting surface progressively increases to a final configuration in which the distal end or follower portion of the instrument is defined by the apex of the conical cutting surface.